fix nullpointer in category search

prototype/src/main/java/org/hso/ecommerce/controller/shop/ShopSearchController.java

@@ -32,9 +32,8 @@ public class ShopSearchController {
     ) {
         model.addAttribute("categories", categoryRepository.getCategories());   //for sidebar
 
-        term = term.trim();
-
         if (term != null) { //if search by Term
+            term = term.trim();
             List<Article> articles = SearchByTermAction.searchByTerm(term, articleRepository);
             model.addAttribute("articles", articles);
         } else if (category != null) {  //if search by Category